PCR-based detection of Vibrio cholerae O139 Bengal with sequences encoding glycosyltransferases.

In a recent publication in this journal, Falklind et al. (2) reported characteristics of DNA sequences encoding glycosyltransferases of Vibrio cholerae O139 Bengal. Their investigations were addressed to ascertain the utility or otherwise of glycosyltransferase-specific PCR primers for obtaining a prompt but specific diagnosis. In their laboratories, PCR emerged as a sensitive procedure with clinical and environmental samples. By nested PCR, employing an additional outer primer pair, O139-3 and O139-4, it was possible to detect about 1 CFU of V. cholerae O139 per assay. The investigators established specificity of their glycosyltransferase region-specific PCR assay by amplification of the genetic material from 240 strains within the family Vibrionaceae and 178 strains of other gram-negative bacteria. PCR amplification was evident only with V. cholerae O139 strains, with no amplification among any of the 384 control strains. Nevertheless, it is essential that specificity of glycosyltransferase PCR technology (2) is also investigated by employing recombinant strains, which have been offered recently for control of cholera in different areas. Prospective investigations of the specificity of glycosyltransferase PCR would be essential with CVD 103-HgR, an attenuated strain of Vibrio cholerae derived from CVD 103, attenuated from the wild-type V. cholerae O1 classical strain, Inaba 569B. In the recombinant CVD 103-HgR, the enzymatically active A subunit of cholera toxin has been deleted and the gene encoding resistance to Hg has been introduced into the hylA locus of the CVD 103 chromosome (3). Furthermore, an attenuated V. cholerae O139 vaccine, Bengal-15, has been prepared recently by deletion of multiple copies of the cholera toxin genetic element from virulent strains of V. cholerae O139. These mutants are also modified by insertion of a construct encoding the B subunit of cholera toxin (1). The specificity would also be evident during amplification of genetic material from Peru-14, an attenuated V. cholerae El Tor mutant with chromosomal deletions in loci of the ctx genetic elements of recA and lacZ (4). Prospective studies of PCR detection of glycosyltransferase genes in CVD 103-Hg4 (3), Bengal-15 (1), and Peru-14 (14), as well as other recombinant strains likely to be offered as vaccines, would vindicate the specificity of the technique, as reported earlier with strains in the family Vibrionaceae and gramnegative bacteria (2).